The polyurethane industry is well underway researching and developing alternative blowing agents for rigid, semi-rigid, and flexible polyurethane foams and microcellular foams which are environmentally friendly while yielding foam properties equivalent to those possess by CFC-blown foams. Many efforts at developing water-blown integral skin foams have met little success because the skin formation has been of poor quality. It is desirable to form a dense, tough skin to provide resistance to abrasion and tear, properties which are particularly important in applications where the foam is subject to frequent manual handling.
These objects are difficult to meet with water-blown foams since carbon dioxide evolved in the chemical reaction between water and isocyanate condenses at relatively high temperatures. Rather than condensing at the mold surface, the carbon dioxide gas escapes from the surface of the foaming mass and out through the vent holes of the mold, forming only a thin skin which peels and easily abrades. Attempts at increasing mold pressure by packing a greater amount of raw material so as to reduce the condensation point of the gas have also not met with success.
In our co-pending application Ser. No. 07/902,137, it was discovered that a certain combination of a modified prepolymer with various resin side ingredients produced an extremely tough and abrasion-resistant skin which exhibited no peeling, porosity, or surface deformities.